title: Ultrafast saturable absorption of two-dimensional MoS2 nanosheets.
abstract: Employing high-yield production of layered materials by liquid-phase exfoliation, molybdenum disulfide (MoS2) dispersions with large populations of single and few layers were prepared. Electron microscopy verified the high quality of the two-dimensional MoS2 nanostructures. Atomic force microscopy analysis revealed that ~39% of the MoS2 flakes had thicknesses of less than 5 nm. Linewidth and frequency difference of the E(1)2g and A1g Raman modes confirmed the effective reduction of flake thicknesses from the bulk MoS2 to the dispersions. Ultrafast nonlinear optical (NLO) properties were investigated using an open-aperture Z-scan technique. All experiments were performed using 100 fs pulses at 800 nm from a mode-locked Ti:sapphire laser. The MoS2 nanosheets exhibited significant saturable absorption (SA) for the femtosecond pulses, resulting in the third-order NLO susceptibility Imχ((3)) ~ 10(-15) esu, figure of merit ~10(-15) esu cm, and free-carrier absorption cross section ~10(-17) cm(2). Induced free carrier density and the relaxation time were estimated to be ~10(16) cm(-3) and ~30 fs, respectively. At the same excitation condition, the MoS2 dispersions show better SA response than the graphene dispersions.
authors.affiliation: Key Laboratory of Materials for High-Power Laser, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences , Shanghai 201800, China.
authors.forename: Kangpeng
authors.initials: K
authors.lastname: Wang
authors.forename: Jun
authors.initials: J
authors.lastname: Wang
authors.forename: Jintai
authors.initials: J
authors.lastname: Fan
authors.forename: Mustafa
authors.initials: M
authors.lastname: Lotya
authors.forename: Arlene
authors.initials: A
authors.lastname: O'Neill
authors.forename: Daniel
authors.initials: D
authors.lastname: Fox
authors.forename: Yanyan
authors.initials: Y
authors.lastname: Feng
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Zhang
authors.forename: Benxue
authors.initials: B
authors.lastname: Jiang
authors.forename: Quanzhong
authors.initials: Q
authors.lastname: Zhao
authors.forename: Hongzhou
authors.initials: H
authors.lastname: Zhang
authors.forename: Jonathan N
authors.initials: JN
authors.lastname: Coleman
authors.forename: Long
authors.initials: L
authors.lastname: Zhang
authors.forename: Werner Josef
authors.initials: WJ
authors.lastname: Blau